Shaft assembly

ABSTRACT

A shaft assembly may include two or more Poka-Yoke bearing caps, each Poka-Yoke bearing cap having a pair of reference bores offset from a central axis of the bearing cap by differing offset distances, and each bearing cap defining a semi-circular recess that is positioned so as to align in use a central axis of the semi-cylindrical recess in the bearing cap with an axis of rotation of a shaft rotatably supported by the bearing cap. The differing offsets of the reference bores prevent the bearing cap from being assembled in a reversed orientation. To ensure that each bearing cap can only be fitted in one position, a centre spacing between the first and second reference bores of each bearing cap is different to the centre spacing used for other bearing caps used to support a single shaft.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to Great Britain Patent Application No.1511413.5, filed Jun. 30, 2015, the entire contents of which are herebyincorporated by reference for all purposes.

FIELD

This invention relates to rotatably supporting a shaft and, inparticular, to a Poka-Yoke bearing cap forming part of a shaft assembly.

BACKGROUND/SUMMARY

It is well known to support a shaft using a split bearing support havingtwo parts defining a bore in which is rotatably supported the shaft.

The assembly of rotating shafts requires split bearing supports withbores that provide very good positional tolerance, cylindricity andconcentricity irrespective of the type of bearing used.

The required accuracy is best met if the split bearing supports are linebored together, that is to say, all concentric bores are machined in oneoperation with all parts in position.

In order to meet functional requirements, it is important that thebearing caps that form one half of the split bearing supports arere-assembled exactly in the same position during engine assembly orduring any subsequent engine servicing.

Various methods have previously been used to ensure each bearing capgoes back in its original position during assembly but these methods donot necessarily prevent mistakes occurring during assembly of thebearing caps. For example, markings can be applied to each bearing capby printing, engraving or casting to help the assembly operator toreplace the bearing caps correctly.

Such markings have a number of disadvantages, for example, printed orengraved markings lead to increased piece price and cast marking fadesand becomes less legible as the casting tool wears out.

For all markings, they provide guidance to the operator but do notprevent mistakes in assembly as the bearing caps can still be assembledthe wrong way round or in the wrong position.

In order to try to overcome such problems it is known from U.S. Pat. No.4,854,746 to provide a bearing cap that is flanked by first and secondshoulders which are asymmetrical in shape and so prevent the bearing capbeing wrongly positioned in a recess defined by precision machined guidesurfaces formed in a bearing support member when a shaft to be supportedis in position.

Although such an arrangement solves some of the problems associated withmarking of the bearing caps it is only appropriate where a precisionmachined recess is formed in the bearing support member. The productionof such a precision machined surface is expensive and time consuming toproduce.

It is an object of the invention to provide a bearing cap that is simpleand cost effective to produce but is so configured as to prevent thebearing cap from being assembled in an incorrect orientation.

It is a further object of the invention to provide a shaft assemblyhaving two or more bearing caps that cannot be assembled in the wrongposition.

According to a first aspect of the invention there is provided a shaftassembly comprising a shaft rotatably supported for rotation about anaxis of rotation by at least two bearing support assemblies, eachbearing support assembly comprising a bearing support structure definingfirst and second reference bores and a first semi-cylindrical recesshaving a central axis, each bearing support assembly further comprisinga bearing cap having first and second feet joined by a bridge portionthat defines a second semi-cylindrical recess for supporting the shaft,the first foot of the bearing cap having a first reference bore formedtherein for accommodating in use a first location dowel and the secondfoot of the bearing cap having a second reference bore formed thereinfor accommodating in use a second location dowel, the first referencebore of the bearing cap being offset from a central axis of the secondsemi-cylindrical recess by a first distance and the second referencebore of the bearing cap being offset from the central axis of the secondsemi-cylindrical recess by a second distance that is different to thefirst distance, each bearing cap being fastened to the bearing supportstructure by a pair of bolts and by the first and second location dowelsengaged with the first and second reference bores in the bearing supportstructure and the first and second reference bores in the bearing cap soas to align the two reference bores in the bearing support structurewith the two reference bores in the bearing cap so that, in use, thecentral axes of the first and second semi-cylindrical recesses in thebearing support structure and the attached bearing cap are bothcoaxially aligned with the axis of rotation of the shaft, wherein eachbearing support assembly has a centre spacing between the alignedreference bores that is different to the centre spacing of any otherbearing support assembly used to support the shaft.

The first foot of each bearing cap may have a first clearance bolt holeextending therethrough for accommodating a first bolt used to secure thebearing cap in use to a corresponding bearing support structure and thesecond foot of each bearing cap may have a second clearance bolt holeextending therethrough for accommodating a second bolt used to securethe bearing cap in use to the bearing support structure, the firstreference bore of each bearing cap may be formed in a mating face of thefirst foot that abuts in use against a first complementary face on thebearing support structure and the second reference bore of each bearingcap may be formed in a mating face of the second foot that abuts in useagainst a second complementary face on the bearing support structure.

The first reference bore of each bearing cap and the first clearancebolt hole of each bearing cap may be coaxially aligned and the secondreference bore of each bearing cap and second clearance bolt hole ofeach bearing cap may be coaxially aligned.

For each bearing cap, the mating face of the first foot and the matingface of the second foot may both lie on a common plane and the first andsecond distances may be measurements from the central axis of the secondsemi-cylindrical recess along the common plane.

For each bearing cap, the first distance may be a measurement of thedistance of a central axis of the first reference bore of the bearingcap from the central axis of the second semi-cylindrical recess and thesecond distance may be a measurement of the distance of a central axisof the second reference bore of the bearing cap from the central axis ofthe second semi-cylindrical recess.

The semi-cylindrical recesses of the bearing support structure and thebearing cap of each bearing support assembly may co-operate in use tosupport a bearing for the shaft.

The bearing may be one of a roller bearing, a ball bearing and a plainbearing. Each bearing support structure may be formed as part of astructural part of an engine.

The first foot of each bearing cap may have first and second clearancebolt holes extending therethrough for accommodating first and secondbolts used to secure the bearing cap in use to the bearing supportstructure, and the second foot of each bearing cap may have third andfourth clearance bolt holes extending therethrough for accommodatingthird and fourth bolts used to secure the bearing cap in use to thebearing support structure.

The first and second clearance bolt holes may be offset from the firstreference bore of the first foot of the bearing cap, and the third andfourth clearance bolt holes may be offset from the second reference boreof the second foot of the bearing cap.

According to a second aspect of the invention there is provided anengine having at least one shaft assembly constructed in accordance withsaid first aspect of the invention. The engine may further comprise acylinder block and a ladderframe bolted to a lower end of the cylinderblock, wherein the ladderframe defines a bearing support structure ofeach bearing support assembly.

The shaft may be one of a crankshaft, a camshaft and a balancer shaft ofthe engine. The shaft assembly may have exactly one shaft, and eachbearing cap may have exactly one semi-circular recess for supporting theone shaft. Further, each bearing cap may have exactly two feet.

According to a third aspect of the invention there is provided a methodof producing a shaft assembly constructed in accordance with said firstaspect of the invention, the method comprising manufacturing a shaft,manufacturing a component having at least two bearing support structureseach of which has a semi-circular recess and first and second referencebores and two or more threaded bores, manufacturing a like number ofbearing caps as there are bearing support structures, each of thebearing caps having a semi-circular recess, first and second referencebores, and two or more bolt clearance holes, wherein the method furthercomprises machining the two reference bores in each bearing cap so thatthe first reference bore is offset from a central axis of the respectivesemi-cylindrical recess by a first distance and the second referencebore is offset from the central axis of the respective semi-cylindricalrecess by a second distance that is different than the first distance,machining the two reference bores in each bearing support structure tomatch the spacing of the first and second reference bores in therespective bearing cap to which it is secured in use, fitting dowels inthe first and second reference bores in the bearing support structuresand the bearing caps, aligning and bringing into mating contact eachbearing cap with the respective bearing support structure so as toproduce full engagement of the dowels with the first and secondreference bores in the bearing caps and bearing support structures,securing the bearing caps to the bearing support structures, andsimultaneously line boring the semi-cylindrical recesses in the bearingsupport structures and bearing caps to produce a bore of a requireddiameter.

The method may further comprise removing the bearing caps from thebearing support structures after the line boring is complete, placingthe shaft and associated bearings in position, replacing the bearingcaps on the matching bearing support structures, and bolting the bearingcaps to the bearing support structures.

Before the line boring, the semi-cylindrical recesses of the bearingsupport structures and bearing caps may each have a first diameter,whereas after the line boring, the semi-cylindrical recesses of thebearing support structures and bearing caps may each have a seconddiameter larger than the first diameter.

Machining each reference bore of the bearing support structures maycomprise machining a chamfered lead-in at a mounting face end thereof,and machining each reference bore of the bearing caps may comprisemachining a chamfered lead-in at a mounting face end thereof. Further,the dowels may comprise chamfers.

Each bearing cap may further comprise first and second bolt clearanceholes in a first foot thereof and third and fourth bolt clearance holesin a second foot thereof. In such examples, machining the first andsecond reference bores in each bearing cap may comprise machining thefirst reference bore at an offset from each of the first and second boltclearance holes and machining the second reference bore at an offsetfrom each of the third and fourth bolt clearance holes.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example with reference tothe accompanying drawing of which:

FIG. 1a is a side view of an engine in accordance with the second aspectof the invention having a shaft assembly constructed in accordance withthe third aspect of the invention, the shaft assembly having two bearingcaps constructed in accordance with the first aspect of the invention;

FIG. 1b is an enlarged view on the line B-B on FIG. 1a in the directionof the arrows;

FIG. 2 is a pictorial view of a bearing cap in accordance with the firstaspect of the invention;

FIG. 3 is a cross-section on an enlarged scale through the bearing capshown in FIG. 2 showing the bearing cap correctly positioned on abearing support structure;

FIG. 4 is a cross-section similar to FIG. 3 but showing a first reversedmisalignment condition of the bearing cap;

FIG. 5 is a cross-section similar to FIG. 3 but showing a secondreversed misalignment condition of the bearing cap;

FIG. 6 is a pictorial view of a ladderframe defining a pair of bearingsupport structures showing the ladderframe in a partially machinedstate;

FIG. 7 is a pictorial view similar to FIG. 6 but showing the ladderframeafter initial machining has taken place with location dowels in positionto accept two bearing caps;

FIG. 8 is a pictorial view similar to FIGS. 6 and 7 showing two bearingcaps in position on the bearing support structures ready for lineboring;

FIG. 9 shows a fully assembled balancer shaft assembly according to theinvention;

FIG. 10a is a side view of an alternative embodiment of bearing cap tothat shown in FIG. 2; and

FIG. 10b is a cross-sectional view on the line V-V on FIG. 10 a.

DETAILED DESCRIPTION

With particular reference to FIGS. 1 a, 1 b, 2 and 3 there is shown anengine 1 having a cylinder head 2, a cylinder block 3 and a ladderframe9 bolted to a lower end of the cylinder block 3. The ladderframe 9defines at a lower end front and rear bearing support structures 7 f, 7r to each of which a respective Poka-Yoke bearing cap 10 f, 10 r isbolted by means of a pair of bolts 25. A front bearing cap 10 f isbolted to the front bearing support structure 7 f and a rear bearing cap10 r is bolted to the rear bearing support structure 7 r.

A shaft 8, which in the case of this example is an engine balancershaft, is rotatably supported by the front and rear bearing caps 10 fand 10 r and the front and rear bearing support structures 7 f and 7 rto form a shaft and bearing assembly. The shaft 8 is rotatably supportedfor rotation about an axis of rotation Z-Z by in the case of thisexample two bearing support assemblies 7 f, 10 f and 7 r, 10 r. However,it will be appreciated that the invention is not limited to the use oftwo bearing support assemblies and that there could be more bearingsupport assemblies than the two provided by way of this example.

The shaft 8 has a drive gear fastened to a front end of the shaft 8 foruse in driveably connecting the shaft 8 to a crankshaft of the engine 1.

Each bearing support assembly therefore comprises of one bearing supportstructure 7 f, 7 r and a respective bearing cap 10 f, 10 r boltedthereto.

A bearing assembly is formed by a bearing support assembly 7 f, 10 f; 7r, 10 r and a respective bearing which in the case of the embodimentshown in FIG. 1b is a plain bearing formed by first and second bearingshells 4, 5 and in the case of the embodiment shown in FIG. 9 is aroller bearing 72.

The two bearing support structures 7 f, 7 r are in terms of constructionsubstantially the same and their general arrangement will be describedhereinafter with reference to the front bearing support structure 7 f.It will be appreciated that the construction and general arrangement ofthe rear bearing support structure 7 r will be substantially the same asthat described with respect to the front bearing support structure 7 f.

The two bearing caps 10 f, 10 r are in terms of constructionsubstantially the same and their general arrangement will be describedhereinafter with reference to the front bearing cap 10 f. It will beappreciated that the construction and general arrangement of the rearbearing cap 10 r will be substantially the same as that described withrespect to the front bearing cap 10 f.

The front bearing support structure 7 f defines a substantiallysemi-cylindrical recess 7 c of radius r′ in which is located one firstbearing shell 4.

The front bearing cap 10 f defines a substantially semi-cylindricalrecess 12 of radius r in which is located one second bearing shell 5.The second bearing shell 5 forms in combination with the first bearingshell 4 a rotary support for the shaft 8.

The front bearing cap 10 f comprises a bridge portion 16 joining firstand second feet 14 and 15 having mating surfaces located on a commonplane x (See FIG. 2). The semi-cylindrical recess 12 is formed in thebridge portion 16 of the bearing cap 10 f between the two feet 14, 15 soas to support the shaft 8 in such a manner that, in use, the axis ofrotation Z-Z of the shaft 8 is arranged coincident with a central axisc-c of the cylindrical recess 12 in the bearing cap 10 f used to supportthe shaft 8. The central axis c-c is positioned at a centre of radius Cof the semi-cylindrical recess 12 (See FIGS. 2 to 5).

The axis of rotation Z-Z of the shaft 8 is, in use, also arranged to becoincident with a centre of radius C′ of the semi-cylindrical recess 7 cin the bearing support structure 7 f. The centre of radius C′ lies on acentral axis of the semi-cylindrical recess 7 c.

A plane Y-Y extends through the centre of radius C of thesemi-cylindrical recess 12 in the bearing cap 10 f, the plane Y-Y isarranged at ninety degrees to the common plane x. The plane x is shownpictorially on FIG. 2 by a dotted line and is indicated by a chaindotted line X-X on FIGS. 3 to 5.

In the example shown, the plane Y-Y is not centrally located withrespect to respective outer edges 14 e, 15 e of the two feet 14, 15.That is to say, the outer edges 14 e, 15 e of the two feet 14, 15 arenot symmetrically arranged with respect to the centre of radius C of thesemi-cylindrical recess 12. However, it will be appreciated that theouter edges 14 e, 15 e of the two feet 14, 15 could be symmetricallyarranged with respect to the axis Y-Y if required because the outeredges 14 e, 15 e of the feet 14, 15 are not used in the case of thisinvention to position the bearing cap 10 f.

The first foot 14 has a first clearance bolt hole 11 a extendingtherethrough and the second foot 15 has a second clearance bolt hole 11b extending therethrough.

In use a bolt 25 is engaged with clearance in the first clearance bolthole 11 a for threaded engagement with a respective threaded bore 7 tformed in the bearing support member 7 f and a bolt 25 is engaged withclearance in the second clearance bolt hole 11 b for threaded engagementwith a respective threaded bore 7 t formed in the front bearing supportmember 7 f, the two bolts 25 are used to fasten the bearing cap 10 f tothe bearing support member 7 f.

The front bearing support member 7 f has first and second referencebores 7 d, 7 e formed therein. The two reference bores 7 d, 7 e areaccurately sized and accurately positioned and are provided for use incorrectly aligning the front bearing cap 10 f with the front bearingsupport structure 7 f.

The reference bores 7 d, 7 e are in the case of this example coaxiallyaligned with the two threaded bores 7 t and are of a larger diameterthan the threaded bores 7 t. However, it will be appreciated that thereference bores and the threaded bores could be offset with respect toone another.

The first clearance bolt hole 11 a in the front bearing cap 10 f has afirst reference bore 13 a formed at one end that in the case of thisexample is coaxially aligned with it. The first reference bore 13 a isformed in the mating surface of the first foot 14 and has a longitudinalcentral axis offset or spaced away from the central axis c-c of thesemi-cylindrical recess 12 in the front bearing cap 10 f by a firstdistance X1 as measured along the plane x.

The second clearance bolt hole 11 b in the front bearing cap 10 f has asecond reference bore 13 b formed at one end that in the case of thisexample is coaxially aligned with it. The second reference bore 13 b isformed in the mating surface of the second foot 15 and has alongitudinal central axis that is offset or spaced away from the centralaxis c-c of the semi-cylindrical recess 12 in the front bearing cap 10 fby a second distance X2 as measured along the plane x.

The two reference bores 13 a, 13 b are accurately sized and accuratelypositioned and are provided for use in correctly aligning the frontbearing cap 10 f with the front bearing support structure 7 f.

The first and second reference bores 13 a, and 13 b are of a largerdiameter than the first and second bolt clearance holes 11 a, 11 b sothat the first clearance hole 11 a and the first reference bore 13 aform a first stepped bore and the second clearance hole 11 b and thesecond reference bore 13 b form a second stepped bore.

It will be appreciated that the two reference bores 13 a, 13 b need notnecessarily be coaxially aligned with the clearance bolt holes 11 a, 11b. FIGS. 10a and 10b show one example of such an offset arrangement.

In accordance with this invention the first and second distances X1 andX2 are never equal to one another and, in the case of this example, thefirst distance X1 is less than the second distance X2. In one exemplaruse of the invention, the distance X1 was chosen to be 0.002 m (2 mm)less than the distance X2 therefore preventing assembly if the bearingcap 10 f is offered up in a ‘reversed orientation’. A ‘reversedorientation’ rotation of the bearing cap 10 f is a rotation of thebearing cap 10 f by 180 degrees about the axis Y-Y from its correctorientation. In order to prevent the bearing caps 10 f, 10 r from beingpositioned on the wrong bearing support structure 7 f, 7 r the centrespacing S between the reference bores 13 a, 13 b in the front bearingcap 10 f is different to that used for the rear bearing cap 10 r.

The centre spacing of the reference bores 13 a, 13 b is the sum of theoffsets X1, X2 from the central axis c-c.

That is to say: S=X1+X2

By way of example and without limitation, Table 1 below provides anexemplary combination of offsets X1, X2 and centre spacings S for a pairof Poka-Yoke bearing caps in accordance with this invention.

TABLE 1 Front Bearing Cap (10f) Rear Bearing Cap (10r) Offset X1 0.033 mOffset X1 0.032 m Offset X2 0.035 m Offset X2 0.034 m Centre Spacing S0.068 m Centre Spacing S 0.066 m

It will be appreciated that the centre spacing of the two referencebores 7 d, 7 e in the bearing support structure 7 f matches that usedfor the bearing cap 10 f so that, in use, the first reference bore 7 din the bearing support structure 7 f is offset the same distance fromthe axis of rotation Z-Z as the first reference bore 13 a in the bearingcap 10 f and the second reference bore 7 e in the bearing supportstructure 7 f is offset the same distance from the axis of rotation Z-Zas the second reference bore 13 b in the bearing cap 10 f.

All of the reference bores 7 d, 7 e, 13 a and 13 b are accuratelymachined and positioned and form along with the dowels 20 the primarylocation means for locating the bearing cap 10 f with respect to thebearing support structure 7 f.

To locate the bearing cap 10 f with respect to the bearing supportstructure 7 f, a dowel bushing 20 is first press fitted into each of thereference bores 7 d, 7 e in the bearing support structure 7 f. Thereference bores 13 a, 13 b in the bearing cap 10 f are then offered upto and engaged with the dowel bushings 20. The bearing cap 10 f is thenpushed into place so that respective mating surfaces on the two feet 14,15 of the bearing cap 10 f abut against complementary end faces on thebearing support structure 7 f Finally, two bolts 25 are inserted throughthe first and second clearance bolt holes 11 a, 11 b and are threadinglyengaged with the threaded bores 7 t in the bearing support structure 7 fto hold the bearing cap 10 f in position.

Prior to assembly of the bearing cap 10 f to the bearing supportstructure 7 f the bearing shells 4, 5 are positioned in the respectivesemi-circular recesses 7 c, 12 and the shaft 8 is then positionedbetween the bearing shells 4, 5 in the support structure 7 f and thebearing cap 10 f respectively ready to be secured in position. The sameassembly steps are used for the rear bearing cap 10 r and the rearbearing support structure 7 r.

Because the offset distances X1 and X2 of the first and second referencebores 13 a, 13 b respectively from the central axis c-c of thesemi-cylindrical recess 12 are different it is not possible to assemblethe bearing cap 10 f to the bearing support structure 7 f in a reversedorientation.

Also because the centre spacing S between the two reference bores 13 a,13 b is different for each bearing cap 10 f, 10 r, the bearing cap 10 fcan only be located on the front bearing support structure 7 f and thebearing cap 10 r can only be located on the rear bearing supportstructure 7 r.

In FIG. 4 the bearing cap 10 f has been reversed compared to its correctorientation shown in FIG. 3. In this case the semi-circular recess 12 inthe bearing cap 10 f has been aligned with the semi-circular recess 7 cin the bearing support structure 7 f, with the shaft 8 in position. Notethat the two reference bores 13 a, 13 b in the bearing cap 10 aremisaligned with the two reference bores 7 d, 7 e in the bearing supportstructure 7 so that it would not be possible to engage the dowelbushings 20 with the reference bores 13 a, 13 b in the bearing cap 10 fif the bearing cap 10 f were to be offered up in this orientation.

In FIG. 5 the bearing cap 10 f has also been reversed compared to itscorrect orientation shown in FIG. 3 but, in this case, the semi-circularrecess 12 in the bearing cap 10 f is misaligned with the semi-circularrecess 7 c in the bearing support structure 7 f, an arrangement that canonly be achieved if the shaft 8 is not in position. Note that the tworeference bores 13 a, 13 b in the bearing cap 10 f are in this casealigned with the two reference bores 7 d, 7 e in the bearing supportstructure 7 f so that it would be possible to engage the dowel bushings20 if it were not for inability to locate the bearing cap 10 f on theshaft 8 due to the misalignment of the semi-circular recesses 7 c, 12.

With reference to FIGS. 10a and 10b there is shown an alternativeembodiment of a bearing cap to that shown in FIG. 2. The bearing cap 110comprises a bridge portion 116 joining first and second feet 114 and 115each of which has a mating surface located on a common plane. Asemi-cylindrical recess 112 is formed in the bridge portion 116 of thebearing cap 110 between the two feet 114, 115 so as to support a shaftin such a manner that, in use, an axis of rotation of the shaft isarranged coincident with a central axis of the semi-cylindrical recess112 in the bearing cap 110.

However, in the case of this embodiment each of the feet 114, 115 hastwo bolt clearance holes 111 a, 111 a′ formed therein so that four boltsin total are used to secure the bearing cap 110 to a respective bearingsupport structure. Each of the feet 114, 115 has a reference bore 113formed therein but in this case the reference bore 113 is not coaxiallyaligned with either of the bolt clearance holes 111 a, 111 a′ but isoffset with respect thereto. As with the embodiment shown and describedwith respect to FIG. 2 two dowels are used to provide alignment of thebearing cap 110 with the bearing support structure to which the bearingcap 110 is bolted in use. A dowel is located in each of the referencebores 113 in the bearing cap 110. The arrangement and spacing of thereference bores 113 is the same as that previously described withrespect to FIG. 2 so that the bearing cap 110 can only be fitted in thecorrect orientation on the correct bearing support structure.

It will be appreciated that the invention is not limited to use with abalancer shaft and is particularly advantageous whenever themanufacturing process requires the assembly, disassembly and re-assemblyof the bearing caps to the bearing support structures.

A method of producing a shaft and bearing assembly in accordance withthe invention will now be described with reference to FIGS. 6 to 9 inwhich the ladderframe 9 is shown inverted to aid manufacture andassembly. In this orientation a gasket surface G of the ladderframe 9faces upwards. The gasket surface G is used to sealingly connect an oilpan to the ladderframe 9 in use. The oil pan would be positioned so asto overlie the balancer shaft 8 at a bottom end of the engine 1.

The method commences with the manufacture of the primary componentsrequired to produce the shaft assembly. This requires manufacture of theshaft 8 using techniques well known in the art, bearings 72 for theshaft to be produced in a conventional manner, the casting of theladderframe 9 and the production of in this case two bearing caps 10 f,10 r.

The bearing caps 10 f, 10 r can be produced by any convenient methodsuch as casting, sintering or machining from solid.

Whatever method is used to produce the ladderframe 9 and the bearingcaps 10 f, 10 r they are all produced at this point in the manufacturingprocess in an unfinished state.

The ladderframe 9 then undergoes a number of further processes thatinclude machining of the base ladderframe 9 to produce desired matingsurfaces such as the gasket surface G, the machining of bearing capmounting surfaces on the bearing support structures 7 f, 7 r, drillingand tapping of the mounting bolt holes 7 t in the bearing supportstructures 7 f, 7 r and the drilling and reaming of two reference bores7 d, 7 e per bearing support structure 7 f, 7 r at the requireddimension and positions to accept at a later stage the dowels 20. Notethat the reference bores 7 d, 7 e preferably include a chamfered lead-in(see FIG. 3) at the mounting face end to facilitate dowel insertion atthe assembly stage.

The semi-cylindrical recesses 7 c are at this stage intentionally leftrough machined at a smaller diameter than that required for the finaldiameter.

The bearing caps 10 f, 10 r are also machined to produce the mountingsurfaces on the two feet 14, 15, are drilled to produce the boltclearance holes 11 a, 11 b and are drilled and reamed to produce the tworeference bores 13 a, 13 b at the required dimensions and positions. Aswith the reference bores 7 d, 7 e the two reference bores 13 a, 13 bpreferably include a chamfered lead-in (see FIG. 3) at the mounting faceend to facilitate the insertion of the dowels 20 at the assembly stage.

The semi-cylindrical recess 12 in each bearing cap 10 f, 10 r isintentionally left rough machined at a smaller diameter than thatrequired for the final diameter.

When all of the basic machining operations are complete the dowels 20are press fitted into the reference bores 7 d, 7 e in the two bearingsupport structures 7 f, 7 r of the ladderframe 9. The insertion of thedowels 20 into the reference bores 7 d, 7 e is facilitated by thepresence of the chamfers (See FIG. 3) on the dowels 20 and the chamfersat the mounting surface ends of the reference bores 7 d, 7 e in thebearing support structures 7 f, 7 r.

The next stage is to assemble the bearing caps 10 f, 10 r onto thebearing support structures 7 f, 7 r of the ladderframe 9 so that thereference bores 13 a, 13 b engage with the pre-assembled dowels 20. Thereference bores 13 a, 13 b are in this case push fit on the dowels 20.That is to say, the reference bores 13 a, 13 b for the dowels 20 aresized so that they provide good positioning but without requiring alarge insertion force to be applied to the bearing caps 10 f, 10 r.

The insertion of the dowels 20 into the reference bores 13 a, 13 b inthe bearing caps 10 f, 10 r is facilitated by the presence of chamfers(See FIG. 3) on the dowels 20 and at the mounting surface ends of thereference bores 13 a, 13 b in the bearing caps 10 f, 10 r.

It will be appreciated that due to the different offsets X1, X2 andcentre spacings S used, the front bearing cap 10 f can only be locatedon the dowels 20 in the front bearing support structure 7 f and the rearbearing cap 10 r can only be assembled onto the dowels 20 in rearbearing support structure 7 r.

Although in this case of this example the dowels 20 are press fittedinto the reference bores 7 d, 7 e and the bearing caps 10 f, 10 r arethen push fitted to the already installed dowels 20 supported by theladderframe 9 it will be appreciated that it would also be possible topress fit the dowels 20 to the bearing caps 10 f, 10 r and then push fitthe dowels 20 into the reference bores 7 d, 7 e in the bearing supportstructures 7 f, 7 r.

Each of the bearing caps 10 f, 10 r is securely fastened in position byin this case two bolts 25. It will however be appreciated that more thantwo bolts could be used to secure each bearing cap in position.

After the bearing caps 10 f, 10 r have been securely fastened inposition, final line boring of the semi-cylindrical recesses 7 c, 12takes place. The machining of all of the bearing support structures 7 f,7 r and the bearing caps 10 f, 10 r is effected at the same time by aline boring operation so as to produce a bore dimension required tosupport, in the case of this example, the roller bearing 72.

The tolerance requirement for the bore formed by the combination of thesemi-cylindrical recesses 7 c, 12 in the bearing support structures 7 f,7 r and the bearing caps 10 f, 10 r respectively is high and so the lineboring may take place in several steps. Initial rough line boring isused to remove most of the unrequired material and then fine line boringis used to achieve the required tolerance. The use of fine line boringhelps to achieve any specific geometrical tolerances required for thebearing support assembly.

After line boring is complete, the bolts 25 are removed and the bearingcaps 10 f, 10 r are removed from the bearing support structures 7 f, 7r.

In the case of this example the dowels 20 will remain in position in thebearing support structures 7 f, 7 r because they are press fitted intothe reference bores 7 d, 7 e but only push fitted to the bearing caps 10f, 10 r.

It will be appreciated that, if the dowels 20 were press fitted in thebearing caps 10 f, 10 r and push fitted to the bearing supportstructures 7 f, 7 r then the dowels 20 will be removed with the bearingcaps 10 f, 10 r and will remain with the bearing caps 10 f, 10 r.

Assembly of the shaft 8 to the ladderframe 9 is as follows: a rollerbearing 72 is positioned on each end of the shaft 8 and the shaft 8 isplaced into position so that the roller bearings 72 lie in thesemi-circular recesses 7 c in the front and rear bearing supportstructures 7 f and 7 r.

In the case of this example, the shaft 8 is shown in FIG. 9 assembled tothe ladderframe 9 prior to assembly of the ladderframe 9 to the cylinderblock 3 of the engine 1. However, it will be appreciated that theladderframe 9 could be assembled onto the cylinder block 3 of the engine1 before the shaft 8 is assembled to the ladderframe 9.

After the shaft 8 along with its bearings 72 has been positioned on thebearing support structures 7 f, 7 r of the ladderframe 9, the bearingcaps 10 f, 10 r are placed back in position. At this stage, thePoka-Yoke nature of the two bearing caps 10 f, 10 r becomes pre-eminentand any attempt to assemble the bearing caps 10 f, 10 r wrongly willlead to either a mismatch between the two semi-cylindrical recesses 7 c,12 or a mismatch between the dowels 20 and the reference bores 13 a, 13b in the bearing caps 10 f, 10 r so that the bearing caps 10 f, 10 rcannot be repositioned incorrectly.

Two securing bolts 25 are then used for each bearing cap 10 f, 10 r tosecure it in position on the respective bearing support structure 7 f, 7r thereby completing the assembly of the shaft 8 to the ladderframe 9.

The Poka-Yoke arrangement of the bearing caps 10 f, 10 r and the bearingsupport structures 7 f, 7 r ensures that the bearing caps 10 f, 10 rcannot be re-assembled in either the wrong orientation or in the wrongposition on the ladderframe 9. That is to say, the front bearing cap 10f can only be fitted to the front bearing support structure 7 f and therear bearing cap 10 r can only be fitted to the rear bearing supportstructure 7 r.

Although the invention has been described herein with reference to itsuse for a balancer shaft it will be appreciated that it could be usedwith advantage for other types of shaft which have multiple bearingssuch as, for example and without limitation, main bearings for acrankshaft, support bearings for a camshaft, support bearings for arotary shaft of a gearbox.

It will also be appreciated that the invention is not limited to usewith a rotating shaft using roller bearings; the invention can beapplied with advantage to shafts using plain bearings or where thebearing caps and the bearing support structures form the bearings for ashaft so that no additional bearings are required.

‘Poka-Yoke’ as meant herein is an arrangement that prevents theincorrect assembly of components.

It will be appreciated by those skilled in the art that although theinvention has been described by way of example with reference to one ormore embodiments it is not limited to the disclosed embodiments and thatalternative embodiments could be constructed without departing from thescope of the invention as defined by the appended claims.

1. A shaft assembly comprising a shaft rotatably supported for rotationabout an axis of rotation by at least two bearing support assemblies,each bearing support assembly comprising a bearing support structuredefining first and second reference bores and a first semi-cylindricalrecess having a central axis, each bearing support assembly furthercomprising a bearing cap having first and second feet joined by a bridgeportion that defines a second semi-cylindrical recess for supporting theshaft, the first foot of the bearing cap having a first reference boreformed therein for accommodating in use a first location dowel and thesecond foot of the bearing cap having a second reference bore formedtherein for accommodating in use a second location dowel, the firstreference bore of the bearing cap being offset from a central axis ofthe second semi-cylindrical recess by a first distance and the secondreference bore of the bearing cap being offset from the central axis ofthe second semi-cylindrical recess by a second distance that isdifferent to the first distance, each bearing cap being fastened to thebearing support structure by a pair of bolts and by the first and secondlocation dowels engaged with the first and second reference bores in thebearing support structure and the first and second reference bores inthe bearing cap so as to align the two reference bores in the bearingsupport structure with the two reference bores in the bearing cap sothat, in use, the central axes of the first and second semi-cylindricalrecesses in the bearing support structure and the attached bearing capare both coaxially aligned with the axis of rotation of the shaft,wherein each bearing support assembly has a centre spacing between thealigned reference bores that is different to the centre spacing of anyother bearing support assembly used to support the shaft.
 2. The shaftassembly as claimed in claim 1, wherein the first foot of each bearingcap has a first clearance bolt hole extending therethrough foraccommodating a first bolt used to secure the bearing cap in use to acorresponding bearing support structure and the second foot of the eachbearing cap has a second clearance bolt hole extending therethrough foraccommodating a second bolt used to secure the bearing cap in use to thebearing support structure, the first reference bore of each bearing capformed in a mating face of the first foot that abuts in use against afirst complementary face on the bearing support structure and the secondreference bore of each bearing cap formed in a mating face of the secondfoot that abuts in use against a second complementary face on thebearing support structure.
 3. The shaft assembly as claimed in claim 2,wherein the first reference bore of each bearing cap and the firstclearance bolt hole of each bearing cap are coaxially aligned and thesecond reference bore of each bearing cap and the second clearance bolthole of each bearing cap are coaxially aligned.
 4. The shaft assembly asclaimed in claim 2, wherein the mating face of the first foot and themating face of the second foot both lie on a common plane and the firstand second distances are measurements from the central axis of thesecond semi-cylindrical recess along the common plane.
 5. The shaftassembly as claimed in claim 4, wherein for each bearing cap, the firstdistance is a measurement of the distance of a central axis of the firstreference bore of the bearing cap from the central axis of the secondsemi-cylindrical recess and the second distance is a measurement of thedistance of a central axis of the second reference bore of the bearingcap from the central axis of the second semi-cylindrical recess.
 6. Theshaft assembly as claimed in claim 1, wherein the semi-cylindricalrecesses of the bearing support structure and the bearing cap of eachbearing support assembly co-operate in use to support a bearing for theshaft.
 7. The shaft assembly as claimed in claim 6, wherein the bearingis one of a roller bearing, a ball bearing and a plain bearing.
 8. Theshaft assembly as claimed in claim 1, wherein each bearing supportstructure is formed as part of a structural part of an engine.
 9. Theshaft assembly as claimed in claim 1, wherein the first foot of eachbearing cap has first and second clearance bolt holes extendingtherethrough for accommodating first and second bolts used to secure thebearing cap in use to the bearing support structure, and the second footof each bearing cap has third and fourth clearance bolt holes extendingtherethrough for accommodating third and fourth bolts used to secure thebearing cap in use to the bearing support structure.
 10. The shaftassembly as claimed in claim 9, wherein the first and second clearancebolt holes are offset from the first reference bore of the first foot ofthe bearing cap, and the third and fourth clearance bolt holes areoffset from the second reference bore of the second foot of the bearingcap.
 11. An engine, comprising: a cylinder block; a ladderframe boltedto a lower end of the cylinder block; a shaft assembly comprising ashaft rotatably supported for rotation about an axis of rotation by atleast two bearing support assemblies, each bearing support assemblycomprising a bearing support structure defined by the ladderframe, eachbearing support structure defining first and second reference bores anda first semi-cylindrical recess having a central axis, each bearingsupport assembly further comprising a bearing cap having first andsecond feet joined by a bridge portion that defines a secondsemi-cylindrical recess for supporting the shaft, the first foot of thebearing cap having a first reference bore formed therein foraccommodating in use a first location dowel and the second foot of thebearing cap having a second reference bore formed therein foraccommodating in use a second location dowel, the first reference boreof the bearing cap being offset from a central axis of the secondsemi-cylindrical recess by a first distance and the second referencebore of the bearing cap being offset from the central axis of the secondsemi-cylindrical recess by a second distance that is different to thefirst distance, each bearing cap being fastened to the bearing supportstructure by a pair of bolts and by the first and second location dowelsengaged with the reference bores in the bearing support structure andthe bearing cap so as to align the first and second reference bores inthe bearing support structure with the first and second reference boresin the bearing cap so that, in use, the central axes of the first andsecond semi-cylindrical recesses in the bearing support structure andthe attached bearing cap are both coaxially aligned with the axis ofrotation of the shaft, wherein each bearing support assembly has acentre spacing between the aligned reference bores that is different tothe centre spacing of any other bearing support assembly used to supportthe shaft.
 12. The engine as claimed in claim 11, wherein the shaft isone of a crankshaft, a camshaft and a balancer shaft of the engine. 13.The engine as claimed in claim 11, wherein the shaft assembly hasexactly one shaft.
 14. The engine as claimed in claim 12, wherein eachbearing cap has exactly one semi-circular recess for supporting the oneshaft.
 15. The engine as claimed in claim 11, wherein each bearing caphas exactly two feet.
 16. A method of producing a shaft assembly,comprising: manufacturing a shaft; manufacturing a component having atleast two bearing support structures each of which has a semi-circularrecess, first and second reference bores, and two or more threadedbores; manufacturing a like number of bearing caps as there are bearingsupport structures, each of the bearing caps having a semi-circularrecess, first and second reference bores, and two or more bolt clearanceholes, wherein the method further comprises machining the two referencebores in each bearing cap so that the first reference bore is offsetfrom a central axis of the respective semi-cylindrical recess by a firstdistance and the second reference bore is offset from the central axisof the respective semi-cylindrical recess by a second distance that isdifferent than the first distance, machining the two reference bores ineach bearing support structure to match the spacing of the first andsecond reference bores in the respective bearing cap to which it issecured in use, fitting dowels in the first and second reference boresin the bearing support structures and the bearing caps, aligning andbringing into mating contact each bearing cap with the respectivebearing support structure so as to produce full engagement of the dowelswith the first and second reference bores in the bearing caps andbearing support structures, securing the bearing caps to the bearingsupport structures, and simultaneously line boring the semi-cylindricalrecesses in the bearing support structures and bearing caps to produce abore of a required diameter.
 17. The method as claimed in claim 16,wherein the method further comprises removing the bearing caps from thebearing support structures after the line boring is complete, placingthe shaft and associated bearings in position, replacing the bearingcaps on the matching bearing support structures, and bolting the bearingcaps to the bearing support structures.
 18. The method as claimed inclaim 16, wherein before the line boring, the semi-cylindrical recessesof the bearing support structures and bearing caps each have a firstdiameter, and wherein after the line boring, the semi-cylindricalrecesses of the bearing support structures and bearing caps each have asecond diameter larger than the first diameter.
 19. The method asclaimed in claim 16, wherein machining each reference bore of thebearing support structures comprises machining a chamfered lead-in at amounting face end thereof, wherein machining each reference bore of thebearing caps comprises machining a chamfered lead-in at a mounting faceend thereof, and wherein the dowels comprise chamfers.
 20. The method asclaimed in claim 16, wherein each bearing cap comprises first and secondbolt clearance holes in a first foot thereof and third and fourth boltclearance holes in a second foot thereof, and wherein machining thefirst and second reference bores in each bearing cap further comprisesmachining the first reference bore at an offset from each of the firstand second bolt clearance holes and machining the second reference boreat an offset from each of the third and fourth bolt clearance holes.